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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
*
* All curves taken from NIST recommendation paper of July 1999
* Available at http://csrc.nist.gov/cryptval/dss.htm
*/
#include "tomcrypt.h"
/**
@file ltc_ecc_mulmod.c
ECC Crypto, Tom St Denis
*/
#ifdef LTC_MECC
#ifndef LTC_ECC_TIMING_RESISTANT
/* size of sliding window, don't change this! */
#define WINSIZE 4
/**
Perform a point multiplication
@param k The scalar to multiply by
@param G The base point
@param R [out] Destination for kG
@param modulus The modulus of the field the ECC curve is in
@param map Boolean whether to map back to affine or not (1==map, 0 == leave in projective)
@return CRYPT_OK on success
*/
int ltc_ecc_mulmod(void *k, ecc_point *G, ecc_point *R, void *modulus, int map)
{
ecc_point *tG, *M[8];
int i, j, err;
void *mu, *mp;
unsigned long buf;
int first, bitbuf, bitcpy, bitcnt, mode, digidx;
LTC_ARGCHK(k != NULL);
LTC_ARGCHK(G != NULL);
LTC_ARGCHK(R != NULL);
LTC_ARGCHK(modulus != NULL);
/* init montgomery reduction */
if ((err = mp_montgomery_setup(modulus, &mp)) != CRYPT_OK) {
return err;
}
if ((err = mp_init(&mu)) != CRYPT_OK) {
mp_montgomery_free(mp);
return err;
}
if ((err = mp_montgomery_normalization(mu, modulus)) != CRYPT_OK) {
mp_montgomery_free(mp);
mp_clear(mu);
return err;
}
/* alloc ram for window temps */
for (i = 0; i < 8; i++) {
M[i] = ltc_ecc_new_point();
if (M[i] == NULL) {
for (j = 0; j < i; j++) {
ltc_ecc_del_point(M[j]);
}
mp_montgomery_free(mp);
mp_clear(mu);
return CRYPT_MEM;
}
}
/* make a copy of G incase R==G */
tG = ltc_ecc_new_point();
if (tG == NULL) { err = CRYPT_MEM; goto done; }
/* tG = G and convert to montgomery */
if (mp_cmp_d(mu, 1) == LTC_MP_EQ) {
if ((err = mp_copy(G->x, tG->x)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(G->y, tG->y)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(G->z, tG->z)) != CRYPT_OK) { goto done; }
} else {
if ((err = mp_mulmod(G->x, mu, modulus, tG->x)) != CRYPT_OK) { goto done; }
if ((err = mp_mulmod(G->y, mu, modulus, tG->y)) != CRYPT_OK) { goto done; }
if ((err = mp_mulmod(G->z, mu, modulus, tG->z)) != CRYPT_OK) { goto done; }
}
mp_clear(mu);
mu = NULL;
/* calc the M tab, which holds kG for k==8..15 */
/* M[0] == 8G */
if ((err = ltc_mp.ecc_ptdbl(tG, M[0], modulus, mp)) != CRYPT_OK) { goto done; }
if ((err = ltc_mp.ecc_ptdbl(M[0], M[0], modulus, mp)) != CRYPT_OK) { goto done; }
if ((err = ltc_mp.ecc_ptdbl(M[0], M[0], modulus, mp)) != CRYPT_OK) { goto done; }
/* now find (8+k)G for k=1..7 */
for (j = 9; j < 16; j++) {
if ((err = ltc_mp.ecc_ptadd(M[j-9], tG, M[j-8], modulus, mp)) != CRYPT_OK) { goto done; }
}
/* setup sliding window */
mode = 0;
bitcnt = 1;
buf = 0;
digidx = mp_get_digit_count(k) - 1;
bitcpy = bitbuf = 0;
first = 1;
/* perform ops */
for (;;) {
/* grab next digit as required */
if (--bitcnt == 0) {
if (digidx == -1) {
break;
}
buf = mp_get_digit(k, digidx);
bitcnt = (int) ltc_mp.bits_per_digit;
--digidx;
}
/* grab the next msb from the ltiplicand */
i = (buf >> (ltc_mp.bits_per_digit - 1)) & 1;
buf <<= 1;
/* skip leading zero bits */
if (mode == 0 && i == 0) {
continue;
}
/* if the bit is zero and mode == 1 then we double */
if (mode == 1 && i == 0) {
if ((err = ltc_mp.ecc_ptdbl(R, R, modulus, mp)) != CRYPT_OK) { goto done; }
continue;
}
/* else we add it to the window */
bitbuf |= (i << (WINSIZE - ++bitcpy));
mode = 2;
if (bitcpy == WINSIZE) {
/* if this is the first window we do a simple copy */
if (first == 1) {
/* R = kG [k = first window] */
if ((err = mp_copy(M[bitbuf-8]->x, R->x)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(M[bitbuf-8]->y, R->y)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(M[bitbuf-8]->z, R->z)) != CRYPT_OK) { goto done; }
first = 0;
} else {
/* normal window */
/* ok window is filled so double as required and add */
/* double first */
for (j = 0; j < WINSIZE; j++) {
if ((err = ltc_mp.ecc_ptdbl(R, R, modulus, mp)) != CRYPT_OK) { goto done; }
}
/* then add, bitbuf will be 8..15 [8..2^WINSIZE] guaranteed */
if ((err = ltc_mp.ecc_ptadd(R, M[bitbuf-8], R, modulus, mp)) != CRYPT_OK) { goto done; }
}
/* empty window and reset */
bitcpy = bitbuf = 0;
mode = 1;
}
}
/* if bits remain then double/add */
if (mode == 2 && bitcpy > 0) {
/* double then add */
for (j = 0; j < bitcpy; j++) {
/* only double if we have had at least one add first */
if (first == 0) {
if ((err = ltc_mp.ecc_ptdbl(R, R, modulus, mp)) != CRYPT_OK) { goto done; }
}
bitbuf <<= 1;
if ((bitbuf & (1 << WINSIZE)) != 0) {
if (first == 1){
/* first add, so copy */
if ((err = mp_copy(tG->x, R->x)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(tG->y, R->y)) != CRYPT_OK) { goto done; }
if ((err = mp_copy(tG->z, R->z)) != CRYPT_OK) { goto done; }
first = 0;
} else {
/* then add */
if ((err = ltc_mp.ecc_ptadd(R, tG, R, modulus, mp)) != CRYPT_OK) { goto done; }
}
}
}
}
/* map R back from projective space */
if (map) {
err = ltc_ecc_map(R, modulus, mp);
} else {
err = CRYPT_OK;
}
done:
if (mu != NULL) {
mp_clear(mu);
}
mp_montgomery_free(mp);
ltc_ecc_del_point(tG);
for (i = 0; i < 8; i++) {
ltc_ecc_del_point(M[i]);
}
return err;
}
#endif
#undef WINSIZE
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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